Process of ahd apparatus for firing ceramic ware



A. s. WATTS 1,724,238

PROGESS OF AND APPARATUS FOR FIRING CERAMIC WARE Original Filed Jan. 29, 1927 2 Sheets-Sheet l ug. 13, 1929. A WATTS 1,724,238

NG CERAMIC WARE Original Filed Jan. 29, 1927' 2 Sheets-Sheet 2 l ATTORNEY.

Patented Aug. 139 1929.

UNITED sritritsV 1,724,238 PATENT OFFICE..

ARTH'URS. W'ATTS, OF COLUMBUS, O-IO.

PROCESS OF AND APPARATUS .FOR FIRING CERAMIC WARE.

Application led January 29, 1927, Serial No. 164,557. Renewed November 8, 1928.

My process of tiring ceramic wares in. a continuous tunnel kiln consists broadly stated, in subjecting the ware to the stages ol biscuiting7 vitriiying, glazing and an` Dealing, and also subjecting the VYare to a temperature drop between any or all ot said stages.

My improved continuous tunnel kiln consists, broadly stated, of distinct zones 'for the various stages of biscuiting, vitriliying7 glazing and annealing, and. a temperature drop zone between any or all o'lA said zones7 whereby any` or all stages of the tiring treatment may be accomplished indepei'ulent of the heat action oil the preceding and suc ceeding stages. Merely 'for the purpose oi? illustrating my invention l have shown a kiln more especially adapted for treating dental porcelain.

In the drawings:

Figure l is a vertical central section through a portion oit a kiln embodying my invention.

Figure 2 is a similar View of the rcmaining portion oi' the kiln.

Figure 3 is a perspectiveview of one ot the sections partly shown in section.

4In the embodiment illustrating my im proved kiln l have shown it as consisting ot fourteen sections numbered 1 to le, inclusive, but as hereinafter'pointed out the number of sections to the kiln may be more or less to adapt it to the heat treatment oit the particular ware being fired.

The sections l, 3, Ll7 (i. 8, l0' and ll have Ventilating tlues l5 which lead in a common liuc 16. The sections l., 3, et, 7, S, 9 and lll; are each provided with baliles 17, the function of each is to control the radiation and circulation from the tunnel portions olZ the kiln to the temperature drop chambers 18.-

The sections 3, 6, 8 and l() each have muli#k fles 19, the construction of which is morek clearly shown in Figure 3. 20 are burners :for said inutiles.

lt will be noted that the temj'ieraturc dro p chambers 1S are provided with vents 2l communicating with. the tlue 1G.

The tunnel 22 of the kiln 'is provided with suitable tracks upon which a car 3 is mounted, said car being adapted to receive the ware and to propel the ware through the length of the kiln. v j f As stated, the kiln is composed of a plurality of detachable sections; each section is supported by suitable frame work mounted on the standards 24,`and between the abutting ends of adjacent sections a suitable interlocking joint is formed to reduce toa minimum radiation of heat at such joints.-

rlhere are certain apparent advantages to be gained by the cooling of many ceramic wares kbetween the stages of (l) biscuiting tiring and vitrifying firing; and, ,(2) be` tween the vitrification tiring and glaze liring; and, between glaze `firing and annealing. A dropping temperature after the biscuit-ing firing causes a shrinkage in the body of the ware, thus aiding in the eliminationof any volatile material trapped in the body through theV contraction of the minute pores contained in the body, as it is niami't'actured. The drop between vitritication and glazing is Valuable because by cooling the body to a reasonable degree the mass would bre retarded as regards heat penetration when exposed to the extremely high temperature of the glazing stage of burning and would be prevented from the overliring which would result from the abrupt passage of the ware from the vitriying zone to the glazing zone. The drop in temperature between the glazing zone and the annealing zone is valuable in thatitreduces the temperature of the ware in order to halt the pyro-chemical process connected with the maturing of the glaze, and thus produce a smoother andA more satisfactory product, atv the same time shortening the space necessary to come into the annealing zone from the glazing zone. This drop must not be so great or abrupt as to injure the product, due to the shock of temperature change. i

ln a normal tunnel kiln tiring process employed in the ceramic industry, theware is subjected toa `gradual temperature increase trom the entrance to thekiln to thel exit from the zone of maximum temperature. This zone of maximum temperatureis usually lo-' cated at about the center ot the kiln, the f passage of t-he ware from themaximum. temperaturc zone 'tothe exit beingemployed as a cooling zonein which the ware gradually radiates its heat so that it emerges from the kiln at a temperature at which `its exposure -to the outside air will not result in injury.

Vithout intending to limit this invention as to when and how the glaze is applied7 it may be accomplishedin a number'V of ways for example, first: after the body of ivare is fired to the desired degree of maturity, then cooled, and the glaze applied as a coating; second: after the body of the Ware is subjected to a sufficient heat treatment to expel organic matter and combined moisture present in the body, and then cooled, the glaze may be applied as a thin coating; third: after the body is merely dried vto eliminate Water` used in preparing and forming the same the glaze may be applied.

rlhe normal ceramic ware contains a certain amount of organic matter and moisture Which are volatilized in the earliest stages of tiring and in the normal tunnel kiln, these volatilized products bathe the ware as it approaches the temperature zone at which volatilization occurs and thus retards 'the free expulsion of the gases generated in the ware during the progressive heating up of the Ware. While it causes a certain contraction of the bulk volume, it also causes anexpansion of the gases present in the Ware, and there is no particular encouragement for these gases to completely escape since no direct suction is provided to urge their removal. According to my invention, the cooling` of the Ware is provided after it has passed this stage in Which the organic matter and moisture are volatilized and before it reaches the stage Where vitrification begins, and the contraction of the Ware due to the temperature drop Will expel a large portion of this entrapped volatile matter.

If the Ware, after passing the maximum temperature zone provided for its vitrification, passes into a zone in which no provision is made for an abrupt temperature drop, the radiation of heat from the surface on Which the Ware rests will be sufficient to overcome the slight radiation from the Ware itself, and the heat action Within 'the body of the Ware Will continue for an indefinite stage, depend. ing on the rate at which the temperature of the Ware lowers, resulting in an overburning of the Ware due to the excessive time for4 which it has been exposed to a temperature at Whichthe vitrifying` action takes place. Y

If the vitrifying'zone merges directly into the glazing zone, the temperature of the glazing zone isl directly additive to the temperature of the vitrifying zone, and the penetration of heat into the body caused Vby the heat applied for the maturing of the glaze may cause an overburning of the bodyv if the temperature required for the maturing of the glaze is sufliciently in excess of the temperature required for the vitrification of the body. Therefore,it is proposed by my invention to-first, halt the temperature inl:rease after the biscuit stage in order to expel the volatilized hydro-carbone and moisture. Second, to halt the temperature increase and provide a temperature drop after the vitrifying zone has been passed so that the interior of the Ware may be sufficiently cooled to retard the penetration of heat to which the ware is exposed in the glazing process beyond the surface of the Ware, and thus prevent an overburning of the interior of the Ware. Third, to provide an abrupt temperature drop after the limited high temperature exposure in the glazing zone so that the heat which penetrates the surface of the Ware in the maturing of the glaze shall have an opportunity to radiate instead of soaking into the body of the ware.

Supplemental to the burning treatment ordinarily provided and to this special high temperature glazing treatment it is proposed to introduce a moderate temperature annealing zone in Which the Ware will be held at a suitable temperature for a suflicient length of time to insure the gradual radiation of'heat Within the mass and allow the cooling treatment to progress Without the development of strains due to a Wide variation in the temperature of the interior and the surface portions of the Ware.

Provisions may be made for the introduction of free air either cold or heated into or around the temperature drop chambers if the particular case requires.

The approximate length of temperature drops in the temperature drop zones will depend upon the purpose of the drop, the size of Ware and composition of the body and the glaze. rlhe temperature drop at the end of the biscuiting stage may be sufficient to cause practically a complete contraction of the Ware to its cold size, thereby encouraging expulsion of gases existing in the Ware through the oxidation of mattei' present when it entered the furnace. (500 to 400 C. more or less.) The temperature drop at the end of the vitrifying zone shall be suiiicient to prevent the heat introduced in the glazing zone from elevating the temperature of the interior of the Ware beyond the temperature attained yin the vitrifying zone. (50O to 400O G. more orless.) The temperature'drop at the end of the glazing zone shall be suiiicient to cause the glaze to harden and prevent injury due to the absorption of gases or other phenomena Which might injure its surface texture during the annealing process and also be sullicient to insure against injury to the body by over heating due to the soaking into the body of the heat introduced in the glazing zone. (5()o or i0()O C. more or less.)

Baflies shall be provided7 if necessary, to controlthe' radiation and circulation from the tunnel portions of the furnace to 'the temperature drop chambers. t will benoted Y that this kiln is builtin sections whereby any zone of the kiln may be changed'as regards length by the introduction or removal. of a section or more, of the standard unit construction. This adjustable feature s prollt? vided in order that the rise in temperature or the drop in temperature most adaptable to the heat treatment of the particular ware being lired may be successfully met.

A suitable insulation of the joints between the sections is provided in order to prevent excessive heat loss where the sections are attached.

My idea is to divide the firing treatment into independent stages oifconduct. However, in a continuous kiln through which the ware travels, I propose to, if necessary, halt the heat treatment at various stages of the firing process resulting in a lowering of the temperature of the ware being burned and incidently causing slight contraction ol' the body which will result in slower penetration of heat into the body when it enters a succeeding heated zone than if it had been carried abruptly from one hot zone to a second hot Zone, the latter being maintained at a higher temperature than the former, or if' the ware is carried from a high temperature Zone abruptly into another heated Zone of slightly lower temperature the soakii'ig action of the heat absorbed in the higher temperature zone will be prevented -from continuing to act upon the ware in the slightly lower temperature zone.

What I claim is:

l. The process et firing ceramic wares in a continuous tunnel kiln which consists in subjecting the ware to the stages of biscuiting, vitrifying, glazing and annealing, and subjecting the ware to a temperature drop between each of the said stages.

2. The process of firing ceramic wares in a single kiln, which consists in subjecting the ware to the stages of loiscuiting, vitriitying, glazing, and annealing, and also subj ecting the ware between some of the stages to a temperature drop.

3. The process of firing ceramic wares in a single kiln which consists in subjecting the ware to the stages of biscuiting, vitriiying, glazing, and annealing, and definitely halting the heat treatment at various stages of the firing process whereby certain physical reactions may be halted `including` a lowerii'ig of the temperature of the body and incidentally a slight contraction of the body, so that the penetration of heat in the succeeding zone may be a process independent of the other heat treatment.

fl. That step in the continuous process of firing ceramic ware in a single kiln, which consists in a temperature drop after the bis-.

cuit firing to cause a shrinkage in the ware,

thereby aiding in the elimination o any volatile material entrapped in the ware through the contraction of the minute pores 'liring ceramic ware in a single kiln, which consists in subjecting the ware to a temperature drop between the glazing and annealing zones, whereby the temperature of the ware is reduced to halt the pyro-chemical process connected with the maturing of the glaze and thus produce a smoother and more satisfactory product, and at the same time shortening `the distance travelled by the warer to come into the annealing zone from the glazing zone. y Y

6. That step in the continuous process o tiring yceramic ware, in a single kiln, which consists in subjecting the ware to a temperature drop between the vitrifying and glazing Zones, to retard heat penetration in the ware when it is exposed to the temperature of glazing and prevent overliring.

V7. That step in the process o'l firing ceramic ware in a continuous kiln built in sections, which consists` in. controlling the heat treatment in the different `zones by changing the length of the various zones through the introduction or removal of a section, or sections.

S. ln a continuous tunnel kiln for firing ceramic ware distinct zones for the various stages of biscuiting, vitrifying, glazing, and annealing, and a temperature drop zone between each of said zones, whereby each stage of the liring treatment may be accomplished independent of the heat action of the preceding and succeeding stages.

9. In a continuous tunnel kiln for firing ceramic ware distinct Zones for the various stages of biscuiting, vitritying, glazing, and annealing, and a temperature drop zone between each of said zones, whereby each stage eli the firing treatment may be accomplished independent oit the heat action of the preceding and succeeding stages, and ballles in the kiln to control the radiation and circulation from the tunnel portions of the furnace to the temperature drop chambers.

10. A. continuous tunnel kiln comprising a plurality of sections detachably secured together, temperature drop chambers in some of said sections, muilles in some of saidA sections, and ventilators leading from some of said sections. n

, 1l.. A continuous tunnel kiln comprising a plurality of sectionsdetachably secured together, ten'iperature drop chambers in` some of said sections, muliles in some` of said sections, and ventilators lea-ding from some 

